The present invention relates to an image carrier cartridge, an exposure head, and an image forming apparatus using these and, more particularly, to an image carrier cartridge with which an organic EL array exposure head as exposure means is united and an image forming apparatus which can be designed to be compact by employing the image carrier cartridge.
In conventional image forming apparatus, such as copying machines, printers, and facsimile machines, utilizing electrophotographic technology, it is common practice to employ a laser scanning optical system as writing means. Under such circumstances, an image forming apparatus has been proposed in Japanese Patent Unexamined Publication No. 2002-23593, in which an EL array exposure head is positioned and arranged in an image carrier cartridge, thereby improving the accuracy in positioning of the EL array exposure head relative to the image carrier. In Japanese Patent Unexamined Publication No. H11-138899, an exposure head has been proposed which employs a single chip on which organic EL light emitting elements are integrated, thereby eliminating variation in light emitting characteristics and reducing the cost. It has been proposed in Japanese Patent Unexamined Publication No. 2002-19176 to hold organic EL light emitting elements and rod lens arrays by a cover preventing the leakage of light.
By the way, in case of employing an organic EL array as writing means of an image forming apparatus, light-emitting parts and driving parts can be disposed together on a single substrate. Therefore, as compared to LED array, higher positioning accuracy of elements and small width between elements can be obtained. However, the organic EL light emitting elements are susceptible to ultraviolet light and thus deteriorated so that the light emitting amount and the light emitting efficiency of the elements are reduced. Especially in case that an organic EL array exposure head is mounted to an image carrier cartridge, the organic EL array exposure head is moved outside of the apparatus and is exposed to outside light together with the image carrier cartridge during replacement of the image carrier cartridge or process for removing a jammed paper. During this, ultraviolet rays from fluorescent lights and/or sunlight are incident on organic EL light emitting material of the organic EL array exposure head so that the organic EL light emitting element(s) may be deteriorated. The deterioration of the organic EL light emitting element(s) leads to reduction in light emitting amount of the deteriorated element(s) and variation in light emitting amount among elements, thus deteriorating the quality of printed image or character.
FIG. 15 is an explanatory illustration showing a course example of light beams emitted from an organic EL light emitting element. In FIG. 15, light beams emitted from the organic EL light emitting element 90 is incident on a transparent substrate 91 so that projected light Rp is projected from a surface opposite to the surface on which the organic EL light emitting element 90 is disposed. Numerals 92, 93 designate frame parts arranged on end faces in the longitudinal direction of the transparent substrate 91. When light beams are projected from the transparent substrate 91, light beams of which incident angle relative to the projection surface exceeds the critical angle are reflected totally at the projection surface. Most of the light beams reflected totally once are projected through the end faces of the transparent substrate 91 after being repeatedly reflected in the transparent substrate 91. The light beams projected through the end faces are stray light beams Rt in the exposure head. Some stray light beams Rt pass an optical system to expose undesired portions on image surface, thus deteriorating the image quality.
To drive the organic EL light emitting element 90, a TFT (thin film transistor) formed on the transparent substrate 91 is employed. The TFT has such a feature that its electrical characteristic varies as light is incident on the TFT. Therefore, if a light beam projected through the end face of the transparent substrate 91 is incident on the TFT as a re-incident light beam Rs, the condition of driving the EL light emitting element 90 is changed, thus unsettling the light emitting amount.